Lifetime and degradation analysis of AgPt alloy thick film/AlN heater for semiconductor wafer annealing

Abstract

In this study, a heater for 300-mm-diameter semiconductor wafer annealing was fabricated by high-temperature firing after screen-printing a silver–platinum (AgPt) paste on an aluminium nitride (AlN) substrate. For life testing, the changes in the electrical characteristics and thermodynamic properties of the Ag65Pt20-alloy thick film on AlN were analysed according to aging by varying the temperature. Ag65Pt20/AlN heater specimens were fabricated to have a resistance of 10 Ω for thermal life tests. The input power was adjusted in the range of 10%–50%, and the temperature was set between 200 °C–600 °C. The Ag65Pt20/AlN heater was aged for approximately 3000 h per unit input power to measure the changes in electrical characteristics. The resistance increased with aging at each temperature and decreased subsequently. The activation energy was 88.7 kJ/(mol·K) [0.92 eV/K]. Moreover, the resistance decreased from the electrode with AgPt metallization, where the bias is applied, to the inner part. Physical analysis of the Ag65Pt20/AlN specimen revealed that the modified Ag65Pt20 alloy exhibited Pt-rich dendrite phases. The separated Pt-rich dendrite phases increased the capacitance. Further, electrical characteristics and material thermodynamic characteristics were analysed through high-temperature aging of the Ag65Pt20/AlN heater. Through such analyses, prognostic health monitoring factors of the Ag-Pt/AlN heater were deduced, thus enabling service lifetime period prediction for predictive maintenance.